From 87c9fe6ee495f78f36d39cb37f6a714444a093ee Mon Sep 17 00:00:00 2001 From: Rafael J. Wysocki Date: Thu, 5 Apr 2018 19:12:43 +0200 Subject: cpuidle: menu: Avoid selecting shallow states with stopped tick If the scheduler tick has been stopped already and the governor selects a shallow idle state, the CPU can spend a long time in that state if the selection is based on an inaccurate prediction of idle time. That effect turns out to be relevant, so it needs to be mitigated. To that end, modify the menu governor to discard the result of the idle time prediction if the tick is stopped and the predicted idle time is less than the tick period length, unless the tick timer is going to expire soon. Signed-off-by: Rafael J. Wysocki Acked-by: Peter Zijlstra (Intel) --- drivers/cpuidle/governors/menu.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-) (limited to 'drivers/cpuidle') diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index 267982e471e0..1bfe03ceb236 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -352,13 +352,28 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, */ data->predicted_us = min(data->predicted_us, expected_interval); - /* - * Use the performance multiplier and the user-configurable - * latency_req to determine the maximum exit latency. - */ - interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load); - if (latency_req > interactivity_req) - latency_req = interactivity_req; + if (tick_nohz_tick_stopped()) { + /* + * If the tick is already stopped, the cost of possible short + * idle duration misprediction is much higher, because the CPU + * may be stuck in a shallow idle state for a long time as a + * result of it. In that case say we might mispredict and try + * to force the CPU into a state for which we would have stopped + * the tick, unless a timer is going to expire really soon + * anyway. + */ + if (data->predicted_us < TICK_USEC) + data->predicted_us = min_t(unsigned int, TICK_USEC, + ktime_to_us(delta_next)); + } else { + /* + * Use the performance multiplier and the user-configurable + * latency_req to determine the maximum exit latency. + */ + interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load); + if (latency_req > interactivity_req) + latency_req = interactivity_req; + } expected_interval = data->predicted_us; /* -- cgit v1.2.3-55-g7522